Contaminant separation

ABSTRACT

A fuel system for a gas turbine engine adapted to handle dirty fuel includes a separating device of a centrifuge-filter type through which fuel is supplied from a fuel pump to combustion apparatus. The centrifuge-filter has a swirl chamber with a tangential inlet, a central annular screen, and outlets both outside and inside of the screen. It discharges a large portion of the fuel substantially clean and a small portion bearing the dirt. The clean fuel flow to small diameter ports of fuel nozzles and, at higher fuel flow rates, through a resistance valve or valves to large area ports of the fuel nozzles. The dirty fuel flows to the large flow ports of the nozzles, by-passing the fuel control. An outlet line from adjacent the outer surface of the screen acts to clean the screen by discharging the finer dirt which tends to accumulate at low flow rates. The separating devices may be arranged in tandem.

United States Patent [1 1 [111 3,718,258 Sharpe [451 Feb. 27, 1973 CONTAMINANT SEPARATION [75] Inventor: Cecil H. Sharpe, Brownsburg, Ind. Primary Examiner-Frank A. Spear, Jr.

Attorney--Paul Fitzpatrick and Jean L. Carpenter [73] Assignee: General Motors Corporation,

Detroit, MlCll. 57 ABSTRACT [22] Filed: 1970 A fuel system for a gas turbine engine adapted to han- Appl. No.: 82,574

Related U.S. Application Data FUEL CONTROL dle dirty fuel includes a separating device of a centrifuge-filter type through which fuel is supplied from a fuel pump to combustion apparatus. The centrifugefilter has a swirl chamber with a tangential inlet, a central annular screen, and outlets both outside and inside of the screen. It discharges a large portion of the fuel substantially clean and a small portion bearing the dirt. The clean fuel flow to small diameter ports of fuel nozzles and, at higher fuel flow rates, through a resistance valve or valves to large area ports of the fuel nozzles. The dirty fuel flows to the large flow ports of the' nozzles, by-passing the fuel control. An outlet line from adjacent the outer surface of the screen acts to clean the screen by discharging the finer dirt which tends to accumulate at low flow rates. The separating devices may be arranged in tandem.

8 Claims, 7 Drawing Figures PATENTED 3.718.258

INVENTOR.

6661/ H S/zarpe BY fizzy ATTOPNFY CONTAMINANT SEPARATION This application is a continuation-in-part of my application Ser. No. 752,820 for Fuel System for Contaminated Fuel filed Aug. 15, 1968 now abandoned.

The invention herein described was made in the course of work under a contract or subcontract thereunder with the Department of Defense.

DESCRIPTION My invention is directed to a fuel system adapted to cope with contaminated or dirty fuel and to render combustion engines capable of operating for substantial periods of time on badly contaminated fuel. Also to means for separating dirt-contaminated liquids' into clean and dirty portions.

The problem arises, for example, in gas turbine engines, in which the fuel is mixed with air by spraying through a nozzle or nozzles which have ports of small diameter which are easily clogged by particles of foreign matter, which may be called dirt.

The obvious mode of attack upon this problem is to provide large filtering systems of very fine pores to intercept and separate the dirt from the fuel before it passes to the engine. This is not feasible because filters clog, thus preventing flow of fuel. There are, of course, systems involving backwashed filters, but these are heavy and the problem of disposing of the dirt-laden fuel remains.

Prior patent applications of Richard G. Grundman and me, for Fuel Nozzle Contaminant Trap, abandoned Ser. No. 617,164 filed Feb. 20, 1967 and Ser. No. 778,002 filed Nov. 14, 1968 U.S. Pat. No. 3,617,001 are directed to a device for intercepting the larger solid particles in the fuel. Our U.S. Pat. No. 3,477,647 for Fuel Spray Nozzle, Nov. 1 1, 1969, discloses a fuel nozzle which is more tolerant of contaminants than those generally known.

It still is desirable, however, to provide other means to reduce the amount of contaminants which pass to the fuel nozzle ports of small diameter. If the amount of contaminant passing to the nozzle is sufficiently small, it may be intercepted by a filter in the nozzle or the supply line to the nozzle. It is also, of course, desirable to minimize the amount of dirt passing through the fuel control of the engine, although the fuel control may be more tolerant of dirt than the small ports of the fuel nozzle.

In aircraft gas turbines, it has been common practice to use fuel nozzles in which atomization is effected by swirling the fuel in a chamber from which it flows over the lip of an opening at one end of the chamber. Because of the wide range of flow, it is usual in aircraft gas turbines to have nozzles of the duplex type with a primary set of fuel swirl ports of small size and a secondary set of swirl ports of relatively large size. The result is that high swirl velocities can be obtained with the small ports at low flow rates, and adequate capacity is provided by used of both sets of ports at high flow rates. Fuel nozzles of this general character are shown, for example, in United States patents to Wortman, U.S. Pat. No. 2,893,647 and to Grundman, U.S. Pat. No. 2,954,172. Fuel flow to the secondary ports may be shut off when the flow rate is small by valve mechanism in the nozzle or by separate control means.

In a system of my invention, which is the subject of my companion patent application Ser. No. 82,573,

filed Oct. 21, 1970, U.S. Pat. No. 3,658,249, the contaminated fuel supplied by a suitable pump is passed through any suitable device or system which acts to separate the fuel into a relatively large flow of substantially clean fuel and a relatively small flow of fuel bearing the larger particles of dirt and, as far as feasible, the smaller contaminant particles also. The clean fuel is supplied through the engine fuel control to the small port or ports of the fuel nozzle or nozzles, which are thus isolated from the dirt. The relatively small portion of dirty fuel, which preferably is controlled by a valve or orifice, flows directly to the large flow ports of the nozzles, by-passing the fuel control and being isolated from the small ports. As a result, the dirty fuel is burned in the combustion chamber of the engine and there is no problem of safety involved in storing or disposing of the contaminated fuel. Also, there is no problem of filter loading.

The preferred separating device, to which this application is directed, is a centrifuge-filter with an annular chamber in which the fuel is swirled from a tangential inlet. A cylindrical screen near the axis of the device encloses the clean fuel outlet. The dirty fuel is discharged at the periphery of the chamber bearing the larger or heavier contaminant particles and most of the finer dirt. Preferably, a further outlet adjacent the outer surface of the screen discharges some fuel bearing finer dirt back to the fuel source or to a point of use to clean the filter.

Principal objects of my invention are to provide means to make fuel control systems and fuel spray systems of usual satisfactory types tolerant of dirty fuel; to provide improved means for separating out major particulate contaminants from liquids; and to provide a centrifuge-filter type device particularly suited to the requirements of practice.

A still further object of the invention is to provide a contaminant separating method and device of improved characteristics, particularly suited to use in a system of the character described.

The nature of my invention and the advantages thereof will be clear to those skilled in the art from the succeeding detailed description of the presently preferred embodiment of the invention and the accompanying drawings thereof.

FIG. 1 is a sectional view of a dirt separating device taken on planes parallel to the axis of a swirl chamber.

FIG. 2 is a schematic diagram of a fuel supply system for a gas turbine engine.

FIG. 3 is a chart illustrating pressure drops.

FIGS. 4 and 5 are schematic diagrams of additional fuel supply systems.

FIG. 6 is a longitudinal sectional view of the preferred filter element for the separator of FIG. 1.

FIG. 7 is a cross-sectional view taken on the plane indicated by the line 7-7 in FIG. 6.

Referring first to FIG. 2, a fuel system embodying my invention may include a fuel inlet line 5 to which fuel is fed from any suitable source such as an aircraft boost pump, a fuel pump 6 which may be driven by the engine, a dirt separating device 7 of a type which may be referred to as a centrifuge-filter, but which will be called herein a separator" for convenience, and a fuel control which may be of any suitable type adapted to control the engine, and may be adjusted by a lever 10.

lt will be clear that the details of the fuel control are entirely immaterial to my invention. The engine to which fuel is supplied ordinarily includes one or more fuel spray nozzles 11, the flow to which is normally controlled by the fuel control.

The fuel control 8 discharges through a line 12 into the separator 7. This device includes a casing 13 defining an annular chamber 14 concentrically within which is mounted an annular filter or screen 15. Line 12 enters the separator tangentially so that the fuel flowing from the pump into the separator swirls around the axis of the separator as indicated by the arrow 17. The major portion of the fuel is discharged from the separator through an axial filtered or clean fuel discharge port 18 within the filter and a clean fuel line 19. Excess fuel supplied to the control over what is metered to the engine is returned to the pump inlet through a line 21. From line 19, the clean metered fuel is delivered through branch lines to the fuel nozzles 11. Each fuel nozzle branch line 20 is connected directly to the portion of the fuel spraying device including the small area, small flow, or primary fuel ports. The nozzle also includes resistance valve means (not illustrated) by which the line 20 is connected to the large area, large flow, or secondary fuel port means of the nozzle.

Such a nozzle may be of the character of those shown in US. Patents to Wortman, US. Pat. No. 2,893,647 and to Grundman, US. Pat. No. 2,954,172. If the engine has one nozzle 11, it may ordinarily incorporate a valve to divert flow from the small flow ports of the nozzle to the large flow ports at high flow rates. If it has a number of nozzles, each may incorporate such a valve; or, if desired, a single resistance valve means may control flow from the manifold 19 to the secondary ports of all the nozzles. As explained in the Wortman and Grundman patents, the valve is held closed by a spring but opens when the pressure in line 20 reaches a value indicative of the fact that the large fuel ports should receive some of the fuel so as not to overload the small fuel ports.

in addition to the fuel supplied from manifold 19 or branch line 20 to the large flow ports of the nozzle, these also discharge the minor fraction of fuel bearing the major particulate contaminant load, which the large flow ports can tolerate. This fuel is supplied from a dirty fuel outlet of the separator 7 through a manifold 22 and branch line 23.

Manifold 22 is connected to the separator 7 through a dirty fuel outlet 24 which is a tangential discharge port extending from the periphery of chamber 14 in the direction of swirl of the fuel. The swirling motion of the fuel tends to concentrate the contaminants at the periphery of chamber 14 and thus direct them into the port 24, and a relatively small portion of the fuel entering the separator is discharged through this port into the dirty fuel line 22. in this line the fuel may proceed through instrumentalities described in my above-mentioned companion application to control or aid flow, which are immaterial to the subject matter of this application. Flow in line 22 may be controlled by an orifice 25. The resistance valve means in the fuel nozzles serves as a check valve to prevent passage of the dirty fuel to the small flow ports of the nozzle.

Proceeding to the separator 7, and referring also to FIG. 1, it will be seen thatthe separator 7 includes a case 13 made up of a main body 27 and a cover 28, the cover being retained on the body by a ring of bolts 29. The case and cover define between them the annular chamber 14 which is sealed by an O-ring 31. The separator inlet is shown at 32 and the clean fuel outlet 18 is in the body.

The preferred filter is a cylindrical screen 15 of finemesh calendered wire cloth, the ends of which are seated in a recess 34 in the cover and a recess 35 in the body, the screen and the recesses being coaxial with chamber 14. The screen 15 is sealingly seated against the body and cover so that fuel can enter outlet 18 only through the screen.

The tangential outlet 24 may be similar to the inlet 32, although preferably of smaller diameter. In operation, the fuel which enters tangentially swirls around in the chamber 14 outside the screen 15, most of it passing through the screen and out through the outlet 18. A small part of the fuel, controlled by orifice 25, flows out the tangential outlet 24, hearing with it the dirt which is centrifuged toward the outer boundary of the chamber 14. The swirling flow of fluid also acts to sweep or wash the outer surfaces of the filter elements to minimize accumulation of dirt or sludge on these surfaces.

it has been found that there is a tendency for a small part of the finer or lighter dirt and lint to miss the outlet 24 and accumulate slowly on the screen, particularly at low flow rates, as when starting the engine. In most cases therefore, it is deemed desirable to include a preferably tangential outlet adjacent the screen and at a point of high flow velocity to remove such fine or light particles from the screen. It is also desirable to have a relatively smooth screen to minimize any tendency for dirt to catch on the screen and aid in maintaining a smooth flow.

As shown in FIGS. 1 and 2, a tangential outlet 36 is provided from recess 34 adjacent the base of the screen to recirculate a small amount of fuel and fine contaminants through a line 38 and a check valve 39 to the pump inlet line 5. This outflow removes dirt from screen 15 which would otherwise accumulate. Flow through line 38 should be controlled at an appropriate value by the capacity of the line or valve 39, or by other means such as a suitable orifice 40.

Experience so far with the separator indicates that improved results are achieved if the diameter of the screen is small relative to that of the chamber 14. This provides better separation and better cleaning of the screen. Very good results have been obtained with a screen of diameter about one-quarter the diameter of the chamber.

In its preferred configuration, the separator 7 relies principally on the centrifugal effect in normal operation rather than straining or filtering, but the screen 15 is a desirable part of the device, particularly in case of very low flows which may occur when starting or stopping the power plant or when idling at high altitudes; also to assist in eliminating that portion of fine dirt that misses outlet 24 in a given pass through the separator.

The structure of the screen 15 is important to the separator. In most filtering systems, the particles are graded to a size by a screen and those which are too large to pass through the screen are trapped there, collected in a receptacle at that point, or washed or back flushed to a receptacle at some point. In my system, particles which will not pass through the screen are kept circulating or moving in the stream. It is quite important that they do not collect on the screen as this will lead to ultimate blockage of the flow.

It is believed that the subject separator is successful in its preferred application because of vortexaction. Flow in the outer portion of the chamber is believed to be functioning as a forced vortex, while that at the core or adjacent the screen functions as a free vortex. Because of this, sufficient energy is available at the screen surface to prevent the collection of dirt and maintain the dirt in suspension in the liquid.

The screen serves a dual purpose. First, it separates the particles due to size; secondly, it acts as a flow straightener which reduces pressure drop. It is considered quite desirable to have a screen structure which will minimize turbulence over and behind it, and it has been found that the presence of the screen significantly reduces the pressure drop in the separator.

The preferred structure of screen 15, which has been worked out by experience for the particular application to gas turbine fuel systems, is shown more particularly in FIGS. 6 and 7. The active part of the screen is a single layer of calendered wire screen 42 having a slight overlap as indicated at 43. The calendering of the wire to provide as nearly as feasible flat outer and inner surfaces is beneficial to the flow. A twenty micron screen opening is employed in this application. The screen 42 is directly supported by a helical coil 44 of wire, which in this case is approximately 0.040 inch in diameter and coiled on about one-tenth inch spacing. The coil is set so that it approaches the outlet end of the screen in the direction of rotation around the axis corresponding to the swirl of the fuel in the chamber 14. This reduces turbulence inside the screen. The upper end of the screen assembly as illustrated in FIG. 6 is the outlet end which is adjacent the outlet 18 illustrated in FIG. 1.

The wire coil is supported and strengthened by a core 46 having two cylindrical end portions 47 and 48 joined by three posts 50. These posts are formed simply by milling three windows through the wall of a unitary cylinder from which the core 46 is machined. The end 47 of the core telescopes into a ring 51 which seats against the bottom of recess 35 and has a groove 52 for an O-ring seal. The other end portion 48 of the core fits over a thimble 54. The parts 46, 51, and 54 may be brazed together with the ends of coil 44 abutting the members 51 and 54. The ends of the cylindrical screen 42 overlie the outer cylindrical surfaces of the ring 51 and thimble 54.

The structure described provides a smooth surfaced screen with sufficient structural integrity to fill the strength requirements and with structure which does not provide crevices in areas in which dirt may collect. The coil 44 adequately supports the very fine screen and provides for smooth flow from the inner surface of the screen into the outlet 18.

The screen structure actually reduces pressure drop, as shown in FIG. 3 which is a graph of experimental determinations of drops through a device as illustrated in FIG. 1, both without the screen and with the screen. It will be noted that with the screen in place the drop is somewhat less than half that without the screen. This apparently is due to the effect of the fine mesh screen in braking the rotation of the fluid around the axis of the separator so that there is no considerable vortex flow on the inside of the screen.

The schematic diagrams of FIGS. 4 and 5 illustrate other separating arrangements embodying centrifugefilters of the type previously described. In the circuits shown in FIGS. 4 and 5, the fuel control 8 is connected in the clean fuel outlet 19 from the separator rather than between the pump 6 and the separator 7. This means that only clean fuel is fed through the fuel control, but the possible disadvantage is that the dirty fuel which is discharged from the separator is not directly metered. If the fuel control 8 in either FIG. 4 or FIG. 5 is of a type which responds directly to a limiting parameter of operation such as temperature or engine speed, the operation is not affected by flow to the engine by-passing the control. Otherwise, some control of such by-passing flow may be needed; but in general this ordinarily would amount to no more than an orifice which would create a predictable amount of by-passing flow which can be compensated for in the calibration of the fuel control 8.

FIG. 4 illustrates an additional feature of the separator itself not shown in the figures previously described and which is optional, depending upon the nature of the installation. This involves providing a second tangential inlet 62 to the separator chamber 14 in addition to the inlet 32 previously described. This inlet is supplied by a branch from the pump outlet line 12 through a resistance valve 63 which opens when the pressure across it rises to a value which indicates that flow into the separator is at a particular substantial level. This feature permits a high injection speed of the fuel into the separator at low rates of flow without creating unduly high resistance to flow as the flow rate increases. In this respect, of course, the operation is similar to that of the resistance valves in fuel nozzles which open a second set of ports as flow rate increases.

FIG. 4 shows a further modification of the system in that the outflow of the dirty fuel from the outlet 36 is not returned to the inlet of pump 6, but instead is added to the main dirty fuel flow into line 22. As indicated in FIG. 4, the outlet 36 adjacent the screen is connected through a line 64 and an orifice 66 to the line 22. The outlet 24 is also connected to line 22 through an orifice 67 which is adapted to control flow from that outlet. This is considered to be advantageous in reducing the work load on the pump in most if not all cases. This ordinarily would not involve sufficient reduction of the flow through line 19 to be material. Also, in some cases, the additional flow might be helpful in washing along the heavier particulate contaminant particles which issue from the separator through outlet 24.

FIG. 5 shows a system which is similar to that of FIG. 4 in that the fuel control is downstream of the separating means and in that the fuel taken from outlet 36 adjacent the screen 15 is directed into the contaminated fuel outlet line 22. So far as this system is as previously described, it will not be described again. The basic difference between FIG. 4 and FIG. 5 lies in the provision of an additional centrifuge-filter or separator 70 which is connected between the pump outlet line 12 and the separator 7. Separator 70 may be identical in structure to the separator 7 except preferably of appreciably smaller size so that it is adapted to attain the desired swirl rates at relatively low flows. It thus has an inlet 32, and outlets 18, 24, and 36 as in the main separator 7. The outlet 18 of the separator 70 is connected through a line 71 to the inlet 32 of separator 70. The outlets 24 and 36 are connected through an orifice 72 to the line 22. Fuel flows from the pump through line 12, separator 70, line 71, andseparator 7 to the clean fuel outlet line 19 during low flow conditions. The separator 7 is essentially idle under these conditions, since the fuel entering it is already clean.

A resistance valve 74 is connected to by-pass the separator 70, connecting pump discharge line 12 directly to the inlet 32 of separator 7. Increasing flow through separator 70 results in a pressure drop which at a suitable level opens resistance valve 74 so that the separator 17 receives not only the clean fuel which is circulated through separator 70 but also a considerable part of the untreated fuel from the pump. At this point the separator 7 acts as previously described. The tandem arrangement of the separators thus provides a means to increase the flow range or improve the performance over an extended flow range, of the separator or separator system. In the arrangement of FIG. 5, the duplicated fuel inlets including the inlet 64 and resistance valve 63 of FIG. 4 are not needed.

FIG. 5 shows still another feature, a by-pass 75 around the main separator 7, controlled by a resistance or relief valve 76. If provided, the purpose of this bypass is to allow fuel to flow in the event that the screen of the separator 7 is blocked by dirt of some sort or other. 1

It will be clear to those skilled in the art that my invention provides a superior system for improving the ability of an engine to operate for substantial periods of time on badly contaminated fuel without significant compromise of the fuel metering and fuel injection components of the engine fuel system. Also, since the dirt-laden fuel is diverted to the fuel nozzle large flow ports and is burned in the normal engine combustion chamber or chambers, there is neither a storage problem nor a hazard from venting the fuel. The centrifuge action relieves the filters of a great part of the burden of separating contaminants, and the swirling of the fuel over the screens provides a filter washing action. Such washing or recirculation of fuel from adjacent the screens prevents clogging of the screens.

While the most important use for my invention is believed to be in connection with aircraft engine fuel systems, it will be clear that the separating apparatuses and methods described may be applied to various installations in which particulate contaminants in a liquid present a problem which can be handled by the use of my invention.

The words filter and screen are used interchangeably herein and are believed to be synonymous in relation to the context of the description and claims.

The detailed description of preferred embodiments of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art without departing from the scope of the invention.

1 claim:

l. A system for separating solid contaminants from a liquid comprising, in combination, a casing defining an annular chamber, an annular fixed filter mounted within and coaxial with the chamber, a tangential inlet to the chamber, means for supplying the liquid to the inlet at sufficient pressure to cause the liquid to swirl within the chamber at substantial velocity adapted to centrifuge the contaminants and to scour the exterior of the filter, a second tangential inlet to the chamber, means for closing one inlet below a predetermined rate of flow of liquid, a discharge port for clean liquid from within the filter, an outlet for a minor portion of the liquid with entrained contaminants departing tangentially from the periphery of the chamber in the direction of the swirl, and means controlling the flow through the said outlet.

2. A system for separating solid contaminants from a liquid comprising, in combination, a casing defining an annular chamber, an annular fixed filter mounted within and coaxial with the chamber, a tangential inlet to the chamber, means for supplying the liquid to the inlet at sufficient pressure to cause the liquid to swirl within the chamber at substantial velocity adapted to centrifuge the contaminants and to scour the exterior of the filter, a second tangential inlet to the chamber, means for closing one inlet below a predetermined rate of flow of liquid, a discharge port for clean liquid from within the filter, an open outlet for a minor portion of the liquid with entrained contaminants departing tangentially from the periphery of the chamber in the direction of the swirl, means controlling the flow through the said outlet, a recirculating outlet radially adjacent the filter, and means for recirculating a portion of the liquid from the recirculating outlet to the said tangential inlet.

3. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having an inlet at the periphery of the chamber directed tangentially of the chamber, means defining a clean liquid outlet substantially on the axis of the chamber, a fixed annular screen coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber across the flow path from the inlet to the outlet, means defining a first tangentially-directed dirty liquid outlet at the periphery of the chamber, and means defining a second tangentially-directed dirty liquid outlet at the outer surface of the screen.

4. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having a first inlet and a second inlet at the periphery of the chamber directed tangentially of the chamber, means responsive to liquid flow level to close one inlet below a predetermined flow level, means defining a clean liquid outlet substantially on the axis of the chamber, a fixed annular screen coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber across the flow path from the inlet to the outlet, means defining a first tangentially-directed dirty liquid outlet at the periphery of the chamber, and means defining a second tangentially-directed dirty liquid outlet at the outer surface of the screen.

5. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, a first centrifuge-filter and a second centrifuge-filter, both centrifuge-filters having a peripheral inlet for liquid, a peripheral outlet for contaminated liquid, and a central outlet for relatively clean liquid, the first centrifuge-filter being of smaller size than the second, means for supplying the liquid to the inlet of the first centrifuge-filter and from the outlet of the first centrifuge-filter to the inlet of the second centrifuge-filter, and means responsive to liquid flow level for conducting a portion of the liquid from the supplying means into the inlet of the second centrifugefilter by-passing the first centrifuge-filter.

6. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, a first centrifuge-filter and a second centrifuge-filter, both centrifuge-filters having a peripheral inlet for liquid, a peripheral outlet for contaminated liquid, and a central outlet for relatively clean liquid, the first centrifuge-filter being of smaller size than the second, means for supplying the liquid to the inlet of the first centrifuge-filter and from the outlet of the first centrifuge-filter to the inlet of the second centrifuge-filter, means responsive to liquid flow level for conducting a portion of the liquid from the supplying means into the inlet of the second centrifuge-filter by-passing the first centrifuge-filter, and means connecting the contaminated fluid outlets of the two centrifuge-filters together.

7. A device for handling a liquid containing particulate contaminants andseparating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having an inlet at the periphery of the chamber directed tangentially of the chamber to direct the liquid into the chamber with swirl, a generally cylindrical annular filter coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber, means defining a clean liquid outlet substantially on the axis of the chamber at one end of the filter, the filter being across the flow path from the inlet to the outlet, and means defining at least one tangentially-directed dirty liquid outlet externally of the filter, the filter comprising an outer annular tubular sheet of calendered wire screen having an array of fine pores distributed over the sheet and having a generally smooth outer surface, and a support for the sheet disposed at the interior of the sheet defining ribs distributed axially of the sheet and extending circumferentially of the sheet, the ribs having a rounded outer surface abuttin the sheet.

8. A device or handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having an inlet at the periphery of the chamber directed tangentially of the chamber to direct the liquid into the chamber with swirl, a generally cylindrical annular filter coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber, means defining a clean liquid outlet substantially on the axis of the chamber at one end of the filter, the filter being across the flow path from the inlet to the outlet, and means defining at least one tangentially-directed dirty liquid outlet externally of the filter, the filter comprising an outer annular tubular sheet having an array of fine pores distributed over the sheet and having a generally smooth outer surface, a support for the sheet disposed at the interior of the sheet defining ribs distributed axially of the sheet and extending circumferentially of the sheet, the ribs having a rounded outer surface abutting the sheet, the support being a helical coil with the helix tending toward the clean liquid outlet in the direction of swirl in the chamber.

2 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,718,258 Dated February 27, 1973 Ihvencor(s) Cecil Sharpe It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

T'- Column 1, line 5 9, "used" should read use 1 Co1umn 8, line 12, :after "an" insert open Signed and sealed. this 27th day of November 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. RENE D. TEGTMEYER Attesting Officer 4 Acting Commissioner of Patents 

1. A system for separating solid contaminants from a liquid comprising, in combination, a casing defining an annular chamber, an annular fixed filter mounted within and coaxial with the chamber, a tangential inlet to the chamber, means for supplying the liquid to the inlet at sufficient pressure to cause the liquid to swirl within the chamber at substantial velocity adapted to centrifuge the contaminants and to scour the exterior of the filter, a second tangential inlet to the chamber, means for closing one inlet below a predetermined rate of flow of liquid, a discharge port for clean liquid from within the filter, an outlet for a minor portion of the liquid with entrained contaminants departing tangentially from the periphery of the chamber in the direction of the swirl, and means controlling the flow through the said outlet.
 2. A system for separating solid contaminants from a liquid comprising, in combination, a casing defining an annular chamber, an annular fixed filter mounted within and coaxial with the chamber, a tangential inlet to the chamber, means for supplying the liquid to the inlet at sufficient pressure to cause the liquid to swirl within the chamber at substantial velocity adapted to centrifuge the contaminants and to scour the exterior of the filter, a second tangential inlet to the chamber, means for closing one inlet below a predetermined rate of flow of liquid, a discharge port for clean liquid from within the filter, an open outlet for a minor portion of the liquid with entrained contaminants departing tangentially from the periphery of the chamber in the direction of the swirl, means controlling the flow through the said outlet, a recirculating outlet radially adjacent the filter, and means for recirculating a portion of the liquid from the recirculating outlet to the said tangential inlet.
 3. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having an inlet at the periphery of the chamber directed tangentially of the chamber, means defining a clean liquid outlet substantially on the axis of the chamber, a fixed annular screen coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber across the flow path from the inlet to the outlet, means defining a first tangentially-dirEcted dirty liquid outlet at the periphery of the chamber, and means defining a second tangentially-directed dirty liquid outlet at the outer surface of the screen.
 4. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having a first inlet and a second inlet at the periphery of the chamber directed tangentially of the chamber, means responsive to liquid flow level to close one inlet below a predetermined flow level, means defining a clean liquid outlet substantially on the axis of the chamber, a fixed annular screen coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber across the flow path from the inlet to the outlet, means defining a first tangentially-directed dirty liquid outlet at the periphery of the chamber, and means defining a second tangentially-directed dirty liquid outlet at the outer surface of the screen.
 5. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, a first centrifuge-filter and a second centrifuge-filter, both centrifuge-filters having a peripheral inlet for liquid, a peripheral outlet for contaminated liquid, and a central outlet for relatively clean liquid, the first centrifuge-filter being of smaller size than the second, means for supplying the liquid to the inlet of the first centrifuge-filter and from the outlet of the first centrifuge-filter to the inlet of the second centrifuge-filter, and means responsive to liquid flow level for conducting a portion of the liquid from the supplying means into the inlet of the second centrifuge-filter by-passing the first centrifuge-filter.
 6. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, a first centrifuge-filter and a second centrifuge-filter, both centrifuge-filters having a peripheral inlet for liquid, a peripheral outlet for contaminated liquid, and a central outlet for relatively clean liquid, the first centrifuge-filter being of smaller size than the second, means for supplying the liquid to the inlet of the first centrifuge-filter and from the outlet of the first centrifuge-filter to the inlet of the second centrifuge-filter, means responsive to liquid flow level for conducting a portion of the liquid from the supplying means into the inlet of the second centrifuge-filter by-passing the first centrifuge-filter, and means connecting the contaminated fluid outlets of the two centrifuge-filters together.
 7. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having an inlet at the periphery of the chamber directed tangentially of the chamber to direct the liquid into the chamber with swirl, a generally cylindrical annular filter coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber, means defining a clean liquid outlet substantially on the axis of the chamber at one end of the filter, the filter being across the flow path from the inlet to the outlet, and means defining at least one tangentially-directed dirty liquid outlet externally of the fIlter, the filter comprising an outer annular tubular sheet of calendered wire screen having an array of fine pores distributed over the sheet and having a generally smooth outer surface, and a support for the sheet disposed at the interior of the sheet defining ribs distributed axially of the sheet and extending circumferentially of the sheet, the ribs having a rounded outer surface abutting the sheet.
 8. A device for handling a liquid containing particulate contaminants and separating the liquid into a major clean portion substantially free of larger particulate contaminants and a minor dirty portion bearing substantially all of the larger particulate contaminants comprising, in combination, means defining an annular swirl chamber having an inlet at the periphery of the chamber directed tangentially of the chamber to direct the liquid into the chamber with swirl, a generally cylindrical annular filter coaxial with the chamber and substantially closer to the axis of the chamber than to the periphery of the chamber, means defining a clean liquid outlet substantially on the axis of the chamber at one end of the filter, the filter being across the flow path from the inlet to the outlet, and means defining at least one tangentially-directed dirty liquid outlet externally of the filter, the filter comprising an outer annular tubular sheet having an array of fine pores distributed over the sheet and having a generally smooth outer surface, a support for the sheet disposed at the interior of the sheet defining ribs distributed axially of the sheet and extending circumferentially of the sheet, the ribs having a rounded outer surface abutting the sheet, the support being a helical coil with the helix tending toward the clean liquid outlet in the direction of swirl in the chamber. 